System for analyzing engine performance

ABSTRACT

A first counter is driven by pulses from a signal generator. A second counter is driven by the output of the signal generator divider by a factor in accordance with the number of cylinders in the engine under test. The output of the second counter is shifted to a register in response to a pulse which is phase synchronized with a predetermined point in the rotation cycle of the engine. The output of the register and the output of the first counter are compared for coincidence, a coincidence signal being generated which corresponds to a predetermined point in the cycle of each of the engine cylinders. These coincidence signals are used to generate window signals which provide gating signals to sensor circuits. The sensor circuits receive the outputs of sensors which provide electrical signals in accordance with various engine parameters. The outputs of the sensor circuits are gated to an indicator by the window signals so that the sensed parameters can be observed at predetermined identifiable portions of each engine rotation cycle.

United States Patent [191 Rennick et al.

[ Dec. 11, 1973 SENSOR CIRCUIT SYSTEM FOR ANALYZING ENGINE PrimaryExaminerJerry W. Myracle PERFORMANCE AttrneyEdward A. Sokolski et al.

[75] Inventors: Lyle V. Rennick, Mission Viejo,

Calif.; John D. Shore, Oconto, Wis; [57] ABSTRACT William L, Mit h l, Fll A first counter is driven by pulses from a signal gener- Calif.;Ronald B. Weiss; Clarence L, ator. A second counter is driven by theoutput of the Almich, both of Anaheim, Calif. signal generator dividerby a factor in accordance with v I the number of cylinders in the engineunder test. The [73] Asslgnee' Nophmp Corporahon Los Angeles' output ofthe second counter is shifted to a register in Ca response to a pulsewhich is phase synchronized with a [22] Filed; Apr, 21, 1972predetermined point in the rotation cycle of the engine. The output ofthe register and the output of the [21] P 246142 first counter arecompared for coincidence, a coincidence signal being generated whichcorresponds to a [52] US. Cl. 73/117.3 Prcdctcrmincd Point in the cycleof each of the engine [51] Int. Cl. G01m /00 cylindcrs- Thesecoincidence s gna s a us d t g n r- [58] Field of Search; 73/116, 117.3are window Signals which pr d gating igna t s nsor circuits. The sensorcircuits receive the outputs of [56] References Cited sensors whichprovide electrical signals in accordance UNITED STATES PATENTS withvarious engine parameters. The outputs of the sensor circuits are gatedto an indicator by the window 523; et 4 3 2 signals so that the sensedparameters can be observed r at predetermined identifiable portions ofeach engine rotation cycle.

t 10 Claims, 4 Drawing Figures 12 14 A I6 17 B 22 PULSE RATE 53 DlvlDERDETECTOR FORMER INTEGRATOR S zi: (z-ro 2B 24 RESET QOUNTER ll I I I 1 l52 5\| 5o COUNTER E551 t l t sauson SENSOR sENsoR REGISTER "'n" *2 *1 iI so 1 IV] 42 l I. EL: J l l COMPARATOR l COUNTER l l l 1 "\D l 32 4%?47 E l l l l 55 i F lwmoow wmoow wmoow SENSOR GENERATOR GENERATORGENERATOR ClRCUlT W'NDOW l *2 #"n" mmcAToR SELECTOR 1 h 34 k i F G r?szuson cmcun' *2 All PATENTED DEC 1 1 I973 sum 2 or 3 PMENTEHHEE I II975 3377.559

SHIET 30? 3 54 I 66 D\ I/ I/ 78 DELAY I I RAMP SAMPLE F.E GENERATOR HOLDCOMPARATOR STROBE (r 7 FROM 77 COMPARATOR COMPARATOR FIG.3 79

wINDow OUTPUT ISTSELECTED RESET wI D0 I 85 8? 92 1 96 H I INTAKE IRECTIF ER GATING L MANIFOLD cIRcurr 'NTEGRATQR 1 so I I COMPARATORcIRcuIT 2 SELECTED I wINDow RESET I II2 I FIG. 4 GATING CIRCUIT!INTEGRATOR 3 I 93 no INDIcAToR SYSTEMFOR ANALYZING ENGINE 2 PERFORMANCEThis invention relates to the analysis of engine operation, and moreparticularly to a digital system capable of indicating various engineoperating parameters during precise portionsof the engine operatingcycle.

In the analysis of the operation of an engine, it is helpful to view andcompare various engine operating parameters during preselectedportionsof the operating cycle. Thus, for example, a malfunctioncan bepinpointed to a particular cylinder, bearing, etc. Mostengine analyzersof the prior art use a cathode ray tube display which is synchronizedwith the firing of the engine cylinders. In view of the'fact that thecylinder firing is generally not reliably and fixedly related to the camshaft and actual cylinder position due to the fact that firing can occurearly or late, this type of prior art device does not provide anaccurate indication of the position of the engine parts when theobservation is made. This type of analysis thus has its limitationswhere precisely accurate measurements need to be made. Further, thescope readout of the prior art requires individual judgment in itsevaluation. 7

The system of this invention overcomes the shortcomings of theaforementioned prior art technique in providing accurate gating windowsfor the various signals representing engine parameters to be evaluated,

these window signals being precisely synchronized withpre-selectedportions of the engine cycle. Further, in the system of this invention,the signals can be automatically evaluated against predeterminedreference voltages so that their departure from acceptable range can beautomatically indicated without any evaluation being necessary on thepart of an operator. Also, means are provided in the system of theinvention to adjust both the width and position of the window within apredetermined range, thus enabling the analysis of a variety of selectedportions of the engine cycle.

It is therefore an object of this invention to provide an improvedengine analyzerin which engine parameters can be monitored at variousprecise selected portions of the operating cycle.

It is another object of this invention to enable the more accuratedetermination of the portion of an engine operating cycle in which amalfunction occurs.

' It is still a further object of this invention to provide a system inwhich automatic indications of out of tolerance operation of an engineare provided.

Other objects of this invention will become apparent as the descriptionproceeds in conjunction with the accompanying drawings, of which:

FIG. 1 is a functional schematic drawing of one embodiment of the systemof the invention;

FIG. 2 is a series of wave forms illustrating the operation of theembodiment of FIG. 1;

FIG. 3 is a functional schematic drawing illustrating a typical windowgenerator of the embodiment of FIG. 1; and

FIG. 4 is a functional schematic drawing illustrating a typical sensorcircuit of the embodiment of FIG. 1.

Briefly described, the system of the invention includes a detector forgenerating a pulse output signal corresponding to a predetermined pointin the engine rotation cycle, such as the top dead center position ofthe No. 1 cylinder. A signal generator is used to generate clock pulsesat a frequency substantially higher than that of the pulse output of thedetector. The output of the signal generator is divided by a factor inaccordance with the number of cylinders in the engine. The divideroutput is fed to a counter, the output of this counter being stored in aregister. The output of the signal generator is fed to a second counter,the outputs of the counter and the register being compared forcoincidence in a comparator. The divider is reset by the pulse output ofthe detector. This reset signal also operates to shift the count of thefirst counter into the register.

The output of the comparator is a pulse signal corresponding topredetermined fractional portions of the enginecycle which in the casewhere the detector output corresponds to the top dead center position ofthe first cylinder will correspond to the top dead center position ofeach of the other. cylinders. The comparator output signals are fedtowindow generators where window signals for gating various sensed outputsignals to an indicator are generated. The window generator-s mayinclude meansfor adjusting the position and width of each of thewindows. The outputs of the window generators are fed to a windowselectorwhich feeds various selected windows to sensor circuits for usein gating the outputs of these circuitsto the indicator. The sensorcircuits may be operated to compare sensor outputs representing variousengine parameters with predeterminedreference voltages representingtolerance limits of these parameters, an output being provided by asensor circuit to the indicator whenever the sensed parameters are notwithin the predetermined tolerances.

Referring now to FIG. 1, one embodiment of the invention isschematically illustrated. A rotating shaft 11 of the engine, which maybe the cam shaft, water pump. drive shaft, etc., which is preciselysynchronized with the rotation of the engine, has a marker 11a thereonwhich precisely indicates a predetermined portion of the engine cycle,such as the top dead center position of the number 1 cylinder. Marker11a may comprise a white spot which reflects light into a photoelectricsensor 12 each time it is directly opposite the sensor. Alternatively,marker 11a may comprise a notch in the shaft with sensor 12 being amagnetic sensor which thus senses a change in magnetic field each timethe notched portion passes.

The output of sensor 12 is fed to pulse former 14, which provides asharp pulse corresponding to the leading edge of the sensed signal, asindicated in Line A of FIG. 2. Thus, a sharp pulse is developed for eachrotation of shaft 11. Pulse former 14 may comprise a differentiatingcircuit, the output of which drives a flipflop. The output of pulseformer 14 is fed to rate integrator 16, which generates a DC voltagedirectly proportional to the output frequency of the pulse former. Theoutput of rate integrator 16 is fed to voltage controlled oscillator 17and controls the frequency of the output thereof which is shown on LineB of FIG. 2. Thus, the frequency of the output of voltage controlledoscillator 17 is automatically adapted in accordance with the frequencyof rotation of shaft 11.

It is to be noted that the frequency of the output of voltage controlledoscillator 17 is not critical and this signal could be generated by awholly independent clock pulse generator. However, the self-adaptationof the frequency of this signal in accordance with the speed of rotationof the engine has the advantage automatically providing the lowest pulsefrequency needed. Thus, for example, when the speed of rotation of theengine is low, the pulse frequency can be correspondingly low for agiven measurement resolution, while as the engine rotation increases,the pulse frequency is increased correspondingly to maintain the sameresolution.

The output of voltage controlled oscillator 17 shown on line B of FIG. 2is fed to counter 20, which may comprisea conventional digital counter.The output of voltage controlled oscillator 17 is also fed to divider 22which divides this frequency by a factor N, corresponding to the numberof cylinders in the engine. The output of divider 22, which is shown onLine C of FIG. 2, is thus for the illustrative example 1/6 of that ofthe output of voltage controlled oscillator 17 (shown on Line B), theengine in this instance being a six-cylinder engine. For aneight-cylinder engine, this factor would be 8, etc.

The output of divider 22 is fed to counter 24. The output of pulseformer 14, which appears once for each rotation of shaft 11, is used asa re-set signal for divider 22, resetting this divider, which maycomprise a binary counter, to zero. This pulse also operates to shiftthe output of counter 24 into register 26. The re-set pulse is also fedto delay flipflop 28 which immediately after the output of counter 24has been shifted into register 26, resets counter 24 to zero. The outputof register 26 is fed to comparator 30, as is the output of counter 20.When the output of counter corresponds to that of register 26, thecomparator generates a pulse output as indicated on Line D of FIG. 2. Ifthe output of pulse former 14 occurs at the top dead center of cylinder1, it should be apparent that the output of comparator 30, as shown onLine D of FIG. 2, will occur precisely at the top dead center positionof each of the cylinders in turn. With coincidence between the pulsecounts fed to comparator 30, a reset signal is fed from the comparatorto counter 20, to reset this counter for a new count.

The output of comparator 30 is fed to each of window generators 32, 34and 36. The number of window generators utilized will depend on theparticular application requirements. Each window generator, as to bedescribedmore fully in connection with FIG. 3, generates a windowsignal, the position of which and width of which may be adjusted. Forexample, an output could be produced for window generator 32 as shown onLine E of FIG. 2, an output for window generator 34 as shown on Line F,and an output for window generator 36 as shown on Line G. It is to beappreciated, however, that a great variety of pulse widths and positionscould be utilized for each of these window'generators, as to beexplained further on in the specification in connection with FIG. 3.

The output of each window generator is fed to window selector 40, whichalso receives the output of sixcount counter 42. Counter 42, whichpreferably provides a visual indication of its count receives the outputof comparator 30 and is reset by the output of pulse former 14. Thus,counter 42, for the illustrative sixcylinder engine example, providesoutputs corresponding to the top dead center position of each of the sixcylinders. The outputs of counter 42 are fed to window selector 40.Window selector may comprise appropriate switching circuits capable ofproviding various combinations of window generator outputs synchronizedwith outputs of counter 42. The outputs of each of the window generatorsmay be provided for any combination or all of the cylinders.

The outputs of window selector 40 are fed to sensor circuits 4749. Eachsensor circuit receives an output from a corresponding one of sensors50-52. The number of sensors and sensor circuits utilized will of coursecorrespond to the number of parameters to be measured. The outputs ofsensors 47-49 are fed to indicator 55, which indicates when the outputof any sensor exceeds predetermined tolerance limits. A typical sensorcircuit is illustrated in FIG. 4 and will be described further on in thespecification in connection therewith.

Referring now to FIG. 3, a typical window generator which may beutilized in the system of the invention is schematically illustrated.The output of comparator 30 (FIG. 1), which is shown on Line D of FIG.2, is fed through delay flipflop to ramp generator 62. Ramp generator62, which may comprise an R-C charging circuit, is discharged to zero inresponse to the output of delay flipflop 60, and thus immediatelythereafter commences its charge cycle to generate a ramp signal as indicated in Line J of FIG. 2. The output of ramp generator 62 is fed bothto sample-hold circuit 64 and comparator 66. The output of thecomparator (Line D of FIG. 2) provides a strobe signal for sample-holdcircuit 1 detect the peak of 64. Sample-hold circuit operates to theramp, this peak ramp signal being placed across potentiometers and 72.The arm of potentiometer 70 is connected to comparator 66, while the armof potentiometer 72 is connected to comparator 77. Potentiometer 70 isused to set the position of the window, while potentiometer 72 is usedto set the width of this window, as now to be explained.

The output of ramp generator 62 is fed to comparator 66 for comparisonwith the voltage at the arm of potentiometer 70. When coincidence isreached between the voltage at the am of potentiometer 70 and the outputof ramp generator 62, comparator 66 actuates switch 78 which maycomprise a transistor switching circuit, to the open" position(indicated in FIG. 3), a positive voltage being generated at the outputof the comparator, as indicated in Line K of FIG. 2. In this manner, thestart of the window and thus its position is determined by the settingof potentiometer 70. It should be immediately apparent that thepotentiometer can be set to cause the window signal shown in Line K ofFIG. 2 to commence anywhere along the ramp (shown in Line J). When theramp cycle is completed, switch 78 returns to the ground position.

The ramp voltage at switch 78, which starts from zero with actuation ofthe switch (in view of the fact that prior to this time the switch is inthe ground position) is fed to comparator 77 for comparison with thevoltage at the arm of potentiometer 72. When this ramp voltage reachesthe voltage set on potentiometer 72, comparator 77 generates a positiveoutput voltage as indicated On Line L in FIG. 2. The output ofcomparator 66 is fed to AND gate 80. The output of comparator 70 isinverted in inverter amplifier 79 and fed to AND gate 80. Thus, whencomparator 66 has a positive output representing a TRUE state, and theoutput of comparator 77 has a zero output which as inverted by means ofamplifier 79, provides a TRUE input to gate 80, the gate will provide aTRUE output as indicated on Line F of FIG. 2. Thus, the width andposition of the window signal, which for the illustrative example isshown on Line F of FIG. 2, is determined by the settings of thepotentiometers 72 and 70 respectively. It thus should be apparent thatthe width and position of the window can be adjusted as desired to meetvarious application requirements.

Referring now to FIG. 4, a typical sensor circuit which may be utilizedin the system of the invention is schematically illustrated. Thisparticular sensor circuit utilizes a microphone which is acousticallycoupled to the intake manifold, exhaust manifold or crankcase to measurethe noise generated thereby which provides an indication of engineperformance. Other types of sensors, such as dynamic pressuretransducers attached to the fuel lines, etc., can be utilized to measurevarious other engine parameters.

The sound present at intake manifold 85 is sensed by microphone 87, theoutput of the microphone being amplified by means of amplifier 89. Atypical output signal which might appear at the output of amplifier 89is shown in Line H of FIG. 2. The output of amplifier 89 is rectified bymeans of rectifier 90,'theoutput of the rectifier being fed to gatingcircuits 92 and 93.'Gating circuit 92 is gated by means of the selectedwindow output of window selector 40 (See FIG. 1). The window selectormay provide a window for any one, any

combination, or all of the cylinders. A typical output signal for gatingcircuit 92 is illustratedin 'Line I of FIG. 2,this signal being for thewindow signal shown on Line F with the No. 3 counter output selected bywindow selector 40 (FIG. 1). The output of thegating circuit isintegrated by means of integrator 96, the output of this integratorbeing fed to comparator circuit 97. Integrator 96 is reset to zero bythe trailing edge of the window signal. A DC reference voltage isprovided at the arm of potentiometer 100, this potentiometer having a DCpower source 101 connected thereacross. With selector switch 105 in theposition shown in FIG. 4, the voltage at the arm of potentiometer 100 isfed to comparator circuit 97 for comparison with the output ofintegrator 96. Potentiometer'lOO is set to provide a voltage at theupper tolerance limits for the noise signal at the intake manifold, suchthat when this tolerance limit is reached, a signal indicating such willbe provided to indicator 110 which may comprise a signal lamp. It

should be immediately apparent that potentiometer 100 can be calibratedto provide any desired tolerance limit.

Gating circuit 93 receives as its gate a second selected window. Theoutput of gating circuit 93 is integrated by means of integrator 1 12,the output of the integrator being fed to potentiometer 113. With switch105 thrown to the position indicated by the dotted line, comparatorcircuit 97 receives the voltage at the arm of potentiometer 113. Thus,the output of integrator 96 is compared with a preselected percentage oftheoutput of integrator 112. In this manner, a comparison can be madebetween the noise developed with the firing of various cylinders withindicator 110 indicating when the ratio between these two signalsexceeds a predetermined value. As for integrator 96, integrator 112 isalso reset by the trailing edge of the window.

The system of this invention thus provides means for indicating theperformance of an engine at precisely defined portions of its operatingcycle.

While this invention has been described and illustrated in detail, it isto be clearly understood that this isintended by way of illustration andexample only, and

is not to be taken by way of limitation, the spirit and scope of thisinvention being limited only by the terms of the following claims.

We claim:

1. In a system for determining the performance of an internal combustionengine having a plurality of cylinders, said system including means forsensing various engine operating parameters, the improvement comprisingmeans for indicating the values of said parameters during a preciselydefined portion of the engine opcrating cycle, comprising:

means for generating a reference pulse signal indicative of apredetermined point in each operating cycle of the engine, means forgenerating a train of pulses, a first counter means for counting theoutput of said pulse train generating means,

divider means for dividing the output of said pulse train generatingmeans by a factor corresponding to the number of cylinders in saidengine,

second counter means'for counting theoutput of said divider means,register means for receiving the output count of said second countermeans,

the output of said reference signal generating means being fed to saidsecond counter means and said register means to provide a reset signaltherefor,

comparator means receiving the outputs of said first counter means andsaid register meansfor generating an output signal when the output ofsaidregister means corresponds to the output of said first countermeans, the output of said comparator means corresponding to theoperating cycle of each of the engine cylinders,

window generator means for generating window signals in response totheoutput of said comparator means,

sensor circuit means for receiving the outputs of said sensing means andgenerating a signalin accordance therewith, said sensor circuit meansincluding a gating circuit, and

indicator means for receiving the outputs of said senmeanscomprisesmeans for providing a reference voltage and means for comparingthe sensing means output with said. reference voltage, said voltagebeing indicative of the tolerance limits of the engine parameter beingmeasured, a signal being provided from said sensor circuit means to saidindicator means whenever the sensing means outputs are not within saidtolerance limits.

4. The system of claim 1 wherein saidwindow generator means includes aplurality of window generators each for generating awindow signal at oneof said =preselected portions of the rotation cycle of the engine, andfurther including window selector means for selecting various windowoutputs of said window generators for use in gating the sensor circuitmeans.

5. The system of claim 4 and further including a counter responsive tothe output of said comparator means forproviding a count correspondingto apredetermined point in the operating cycle of each of the cylindersof the engine, the output of said counter being fed to said windowselector means for use in gating the window signals to said sensorcirucit means.

6. The system of claim 1 wherein said means for generating a train ofpulses comprises a voltage controlled oscillator and a rate integratorfor generating a voltage for controlling said voltage controlledoscillator, said rate integrator operating in response to said referencepulse signal, whereby the frequency of the output of said voltagecontrolled oscillator is in accordance with the rotation speed of theengine.

7. A system for providing signals indicative of the operating conditionof an internal combustion engine having a plurality of cylinders duringpreselected portions of the operating cycle of said engine comprising:

means for generating a reference pulse signal synchronized with apredetermined point of said cycle, means for generating a train of clockpulses,

divider means for dividing said train of pulses by a factorcorresponding to the number of cylinders in said engine, 4

first counter means for counting the output of said divider means,

a register for registering the count in said first counter in responseto the output of said reference pulse signal generating means,

second counter means for counting the pulses in said clock pulse train,

means for delaying said reference pulse, the output of said delayingmeans being fed to said first counter means to reset said first countermeans,

comparator means for comparing the output of said second counter withthe output of said register and for generating a pulse output when theseoutputs correspond,

window generator means responsive to the pulse output of said comparatormeans for generating a window signal in a predetermined phaserelationship with said last mentioned pulse output,

sensor means for sensing an operating parameter of the engine,

sensor circuit means for generating an output signal in accordance withthe sensor means output, said sensor circuit means including a gatingcircuit, said window signal being fed to the gating circuit of saidsensor circuit means to gate said output signal, and indicator means forindicating said output signal.

8. The system of claim 7 wherein said window generator means includesmeans for adjusting the position and width of the window. I

9. The system of claim 7 wherein said means for generating a train ofclock pulses comprises a voltage controlled oscillator and a rateintegrator connected to said oscillator for generating a voltage forcontrolling said oscillator, said rate integrator operating in responseto said reference pulse signal.

10. The system of claim 7 wherein said sensor circuit means comprisesmeans for providing a reference voltage indicative of the tolerancelimits of the parameter sensed by said sensor means and means forcomparing the sensor means output with said reference voltage, a signalbeing provided to said indicator means whenever the sensor means outputsare not within said tolerance limits.

1. In a system for determining the performance of an internal combustionengine having a plurality of cylinders, said system including means forsensing various engine operating parameters, the improvement comprisingmeans for indicating the values of said parameters during a preciselydefined portion of the engine operating cycle, comprising: means forgenerating a reference pulse signal indicative of a predetermined pointin each operating cycle of the engine, means for generating a train ofpulses, a first counter means for counting the output of said pulsetrain generating means, divider means for Dividing the output of saidpulse train generating means by a factor corresponding to the number ofcylinders in said engine, second counter means for counting the outputof said divider means, register means for receiving the output count ofsaid second counter means, the output of said reference signalgenerating means being fed to said second counter means and saidregister means to provide a reset signal therefor, comparator meansreceiving the outputs of said first counter means and said registermeans for generating an output signal when the output of said registermeans corresponds to the output of said first counter means, the outputof said comparator means corresponding to the operating cycle of each ofthe engine cylinders, window generator means for generating windowsignals in response to the output of said comparator means, sensorcircuit means for receiving the outputs of said sensing means andgenerating a signal in accordance therewith, said sensor circuit meansincluding a gating circuit, and indicator means for receiving theoutputs of said sensor circuit means and providing an indicationthereof, the window signals being fed to the gating circuit of saidsensor circuit means to gate the outputs thereof to said indicator meansat preselected portions of the rotation cycle of said engine.
 2. Thesystem of claim 1 wherein said window generator means includes means foradjusting the width and position of the window.
 3. The system of claim 1wherein said sensor circuit means comprises means for providing areference voltage and means for comparing the sensing means output withsaid reference voltage, said voltage being indicative of the tolerancelimits of the engine parameter being measured, a signal being providedfrom said sensor circuit means to said indicator means whenever thesensing means outputs are not within said tolerance limits.
 4. Thesystem of claim 1 wherein said window generator means includes aplurality of window generators each for generating a window signal atone of said preselected portions of the rotation cycle of the engine,and further including window selector means for selecting various windowoutputs of said window generators for use in gating the sensor circuitmeans.
 5. The system of claim 4 and further including a counterresponsive to the output of said comparator means for providing a countcorresponding to a predetermined point in the operating cycle of each ofthe cylinders of the engine, the output of said counter being fed tosaid window selector means for use in gating the window signals to saidsensor cirucit means.
 6. The system of claim 1 wherein said means forgenerating a train of pulses comprises a voltage controlled oscillatorand a rate integrator for generating a voltage for controlling saidvoltage controlled oscillator, said rate integrator operating inresponse to said reference pulse signal, whereby the frequency of theoutput of said voltage controlled oscillator is in accordance with therotation speed of the engine.
 7. A system for providing signalsindicative of the operating condition of an internal combustion enginehaving a plurality of cylinders during preselected portions of theoperating cycle of said engine comprising: means for generating areference pulse signal synchronized with a predetermined point of saidcycle, means for generating a train of clock pulses, divider means fordividing said train of pulses by a factor corresponding to the number ofcylinders in said engine, first counter means for counting the output ofsaid divider means, a register for registering the count in said firstcounter in response to the output of said reference pulse signalgenerating means, second counter means for counting the pulses in saidclock pulse train, means for delaying said reference pulse, the outputof said delaying means being fed to said first counter means to resetsaid first counter means, comparator Means for comparing the output ofsaid second counter with the output of said register and for generatinga pulse output when these outputs correspond, window generator meansresponsive to the pulse output of said comparator means for generating awindow signal in a predetermined phase relationship with said lastmentioned pulse output, sensor means for sensing an operating parameterof the engine, sensor circuit means for generating an output signal inaccordance with the sensor means output, said sensor circuit meansincluding a gating circuit, said window signal being fed to the gatingcircuit of said sensor circuit means to gate said output signal, andindicator means for indicating said output signal.
 8. The system ofclaim 7 wherein said window generator means includes means for adjustingthe position and width of the window.
 9. The system of claim 7 whereinsaid means for generating a train of clock pulses comprises a voltagecontrolled oscillator and a rate integrator connected to said oscillatorfor generating a voltage for controlling said oscillator, said rateintegrator operating in response to said reference pulse signal.
 10. Thesystem of claim 7 wherein said sensor circuit means comprises means forproviding a reference voltage indicative of the tolerance limits of theparameter sensed by said sensor means and means for comparing the sensormeans output with said reference voltage, a signal being provided tosaid indicator means whenever the sensor means outputs are not withinsaid tolerance limits.